For some, not all, of those travelers to Spain the situation is more complicated than, "I want to do a pub crawl in Benidorm."
There are about 300k Brits living in Spain - some will be parents, grandparents, kids. There are plenty of British/Spanish families around. Around a million Brits own property the. That brings personal ties and business/organisational issues for lots of people.
Personally, I may not be that sympathetic to the tourists (not even those just traveling within Spain!) who are reigniting the epidemic by travelling from high incidence areas to low, or from social distancing to "all bets are off" in clubs and bars. But I do understand that for a good number of them, the trip will have been about more than that.